Chronic obstructive pulmonary disease (COPD) is a common disease that results in considerable morbidity and mortality. Epidemiological studies indicate that persons with COPD are particularly susceptible to the effects of traffic related particles. To date, our knowledge regarding these effects is mostly derived from community-based epidemiologic studies using administrative databases and population exposures. Epidemiological observations indicating effects in large population samples have not yet been demonstrated in patients with COPD and the mechanisms of disease remain uncertain. Previous efforts to study the health effects of air pollution in patients with COPD have been limited by inadequate sample size, an inadequate assessment of personal exposure, and lack of a suitable cohort. We have addressed these limitations and will study the effects of traffic-related pollution in 300 persons with moderate to severe COPD recruited from patients receiving clinical care at VA Boston. We hypothesize that when assessed over one year, exposure to traffic-related particles as measured by black carbon will result in exacerbations of COPD, a reduction in pulmonary function, an increase in measures of systemic inflammation, and an increase in systemic oxidative stress in a dose-related manner. Exposure will be assessed by a Boston-area black carbon spatio-temporal land use regression model with model validation by in-home monitoring The information obtained from this research project will define the exposure response relationships between traffic-related particles and the clinical, pulmonary, and systemic responses to air pollution in patients with COPD.